1. Field of the Invention
The present invention relates to a bidirectional elastic store circuit and more particularly, to an elastic store circuit capable of transmitting and receiving data in a bidirectional manner with a simple structure.
2. Description of the Prior Art
An elastic store circuit in the field of data communication is generally used for the purpose of multiplexing, data signalling rate conversion, phase variation absorption and the like. A large capacity of elastic store circuit in which store cells are arranged in a matrix manner is disclosed in, for example, Japanese Patent Publication Gazette No. 45544/1981.
FIG. 1 is a schematic block diagram showing a structure of a conventional elastic store circuit.
Description is now made on the structure of the conventional elastic store circuit shown in FIG. 1. In FIG. 1, an elastic store portion 1 comprises an address decoder (not shown), store cells (not shown) and the like, and has an input terminal 2 receiving a signal WR for initializing the write address of the elastic store portion 1 and an input terminal 3 receiving a signal RR for initializing the read address of the elastic store portion 1. In addition, a data input DI is applied to the elastic store portion 1 through an input terminal 4 and a data output DO of the elastic store portion 1 is outputted through an output terminal 5. Furthermore, a logical element 7 is connected between the elastic store portion 1 and the output terminal 5 so as to enable a wired OR function. The logical element 7 is controlled by a chip selecting signal CS inputted from a chip selecting signal input terminal 6.
Description is now made on operation of the conventional elastic store circuit shown in FIG. 1. The data DI inputted through the input terminal 4 is written into each store cell (not shown) constituting the elastic store portion 1 while the address is controlled by the write address initialization signal WR applied through the input terminal 2. At the time of read-out, the data DO is read out from each store cell and is outputted through the output terminal 5 while the address is controlled by the read address initialization signal RR applied through the input terminal 3. The data output DO is selected by the chip selecting signal CS applied to the chip selecting signal input terminal 6, so that the wired OR function is achieved.
However, since the conventional elastic store circuit has only a single data input terminal and a single data output terminal as described above, it can be used only for data transmission and reception in a single direction. Therefore, when it is intended to be used for a bidirectional data communication system, at least two elastic store circuits are required to receive and transmit data in a first direction and receive and transmit data in a second direction opposite to the first direction, so that the number of components of the system is increased and the system becomes expensive.